Multipass evaporator



1964 G. c. RANNENBERG 3,161,234

MULTIPASS EVAPQRATOR Filed Oct. 16, 1962 2 Sheets-Sheet 2 6 i 5. i w

United States Patent Office 3,ldl,234 Patented Dec. 15, 1964 3,1dl,2 34MULTEPASS APBQRATQR George C. Rannenherg, Granhy, ilonn, assignor toUnited Aircraft Qorporation, East Hartford, Quinn, a corporation ofDelaware p Filed Set. 16, 1962, Ser. No. 230,818 6 Qlaims. Cl. 165--163)This invention relates to heat exchangers and more particularly toevaporators adapted to be used in a refrigeration system.

As is well known, an evaporator is that part of a refrigeration systemwhere the refrigerant enters the evaporator as a liquid and is vaporizedto produce refrigeration. As the air passes through the evaporator, itcomes in indirect heat exchange relation with the refrigerant, gives upits heat thereto and is discharged at a much lower temperature than itwas when entering the evaporator.

The temperature of the refrigerant decreases as a function of its lengthof travel in the evaporator until it reaches a particular pointintermediate the inlet and outlet of the evaporator. At this point, theliquid refrigerant vaporizes and becomes superheated and hence becomeshotter as it continues its travel. The temperature of the refrigerantincreases until it reaches the outlet of the evaporator. Conventionalrefrigerant evaporators constructed of tubes are often arranged to takeadvantage of this feature by locating the first refrigerant passintermediate the refrigerant inlet and refrigerant outlet of theevaporator. In addition, the air to be cooled is first placed inindirect heat exchange relation with the fourth pass (Where thetemperature of the refrigerant is at its hottest value) and the thirdpass is placed in indirect heat exchange relation with the air leavingthe evaporator. The second pass is sandwiched between the first andthird pass. In this manner, maximum temperature differences for heattransfer between the refrigerant and the hot air intended to be cooledare maintained with resultant maximum utilization of the heat exchangersurface area. By the innovation of this invention, I am able to obtainmaximum utilization of heat exchanger surface area with a plate-finconfiguration. as was obtainable heretofore only with tube bundleconfigurations. The plate-fin evaporator made possible by this inventionhas the advantage of lower weight and volume than that required byprevious conventional plate-fin evaporators.

It is the object of this invention to provide in an evaporator, asdescribed, a novel arrangement of the headers of the evaporator, whichinclude locating external headers one within the other with a commonwall separating each, combining external headers with internal headers,and locating the headers internally, so as to obtain maximum temperaturedifference for heat transfer.

Other features and advantages will be apparent from the specificationand claims and from the accompanying drawings which illustrate anembodiment of the invention.

FIG. 1 is an isometric view of a portion of the evaporator showing anarrangement in which internal and external headers are used.

FIG. 2 is a cross-sectional view taken along line 22 of FIG. 1,particularly showing the novel location of the refrigerant passes.

FIG. 3 is a schematic illustration showing the novel arrangement ofexternal headers, one inside the other.

FIG. 4 is a schematic illustration wherein all the headers are internal.

Now referring to the drawings, FIG. 1 shows a portion 7 of the core ofthe evaporator generally illustrated by numeral fill and a pair of airpasses indicated by the jnumerals i2 and 14 sandwiching the refrigerantcore elerneral 16. As is noted from the drawing, this section of thecore has been exploded to illustrate the inventive concept, but onlyrepresents a portion of the entire core. It should be understood thatthe entire evaporator is built up by alternately stacking similar airand refrigerant core elements to obtain the size necessary to affordoptimum refrigeration in any given application.

As will be appreciated by one skilled in the art, the generalconstruction of the evaporator may take any conventional form, however,the plate-fin type of heat exchanger is often preferred for reasons oflow weight and volume. As noted in FIG. 1, the partial core comprisesend plate 16 and dividing walls 18, 26 and 22 extending longitudinallythrough the evaporator. Generally parallel fin section 24 is sandwichedbetween end plate 16 and dividing wall 18 for defining an air pass. Thegenerally parallel fin section 24 may be pierced, serrated, rufiled orstraight, depending on such matters as economics and the fluidsinvolved. Closure bars 28 and 30, also extending longitudinally, definepassage chambers for receiving the fins so that the fins, together withthe end plate, dividing wall and closure bars define a passage for theair intended to be cooled. The air is admitted at the top end of theevaporator and is discharged at the bottom in FIG. 1, although anyorientation with gravity may be used. Similarly, another air passage,shown in FIG. 1, is formed from a pair of dividing walls 29 and 22,closure members 32 and 34 and the heat transfer fins 26.

The refrigerant passes, located between a pair of air passes, comprise asimilar plate-fin construction, only extending transversely of the airpasses. Since the actual construction of the evaporator may take anywell-known form, a description thereof, for the sake of convenience, isomitted.

Reference is now made to FIG. 2, which illustrates the novel arrangementof the refrigerant passes. As shown in FIG. 2, the refrigerant isadmitted into the evaporator through a plurality of tubes, indicated bynumeral 34, which lead into header 36. The header directs the flowthrough the first pass, indicated by Letter A. In accordance with thepresent invention, the first pass is located intermediate the top andbottom closure plates of the refrigerant core. As indicated above, thepass comprises a plurality of fins which extend between the dividingplates 13 and 20. Turning passages 37, defined by fins, are mounted atthe far end of the inlet and direct the refrigerant to the second pass Band similarly, turning fins B located between the third pass C and thesecond pass B direct refrigerant to the third pass. Finally, therefrigerant feeds into an external header 41 which conducts therefrigerant in the third pass to the fourth pass D. The refrigerant,which at this point has vaporized and become superheated, is dischargedinto the outlet header 44 and then directed through the dischargeconduit 46 to the next stage (not shown) in the refrigeration system.

It will be noted that each pass may contain a different number ofpassages, and preferably, the number of passages in each pass areincreased as the liquid is vaporized. Thus, the liquid passing throughthe evaporator remains a liquid until it reaches the end of the third orthe beginning of the fourth pass. Thus, by virtue of the novelarrangement of the passes, the hot air entering the evaporator isimmediately in indirect heat exchange relation with the superheatedrefrigerant passing through pass D. As the air becomes cooled, it passesin indirect heat exchange relationship with the liquid refrigerant inpasses A and B, and finally theair passes over the lowest temperaturerefrigerant as it reaches pass C. after'which the air.

is completely refrigerated.

From the foregoing, it will be appreciated that the air intended to becooled when at its hottest temperature,

comes into indirect heat relation with the refrigerant at its hottesttemperature.""While, obviously the heat differential between the hot airand the refrigerant at its coolest, temperature would beatitsgreatestvalue, yet from the standpoint of the overalltemperatureditferential of all the passes, the temperature difierentialobtained by the arrangement shown by'the present invention is higher.Because of this feature,.the evaporator has a highheat transferefiiciency and hence achieves minimum heat exchanger or evaporator sizefor 'agiven application.

' FIGS. 3 and 4 are exemplaryshowings of a refrigerant core elementembodying the t' present' invention,- but,eni-' ploying diiferent headerarrangements; .Various factors,

such as the shape of the volume available for th'e evaporator,materials, and brazing capabilities will determine detailed arrangementselected. Again, for. the sake of convenience, reference to theconstruction and the details of the core elements are omitted. It willbe appreciated, however, that the mechanical details of construction ofthe core can be of any well-known, plate-fin form. As in FIGS. 1 and 2,the construction of the core elements shown in FIGS. 3 and 4 are of theplate-fin type. Also, it will be appreciated that the location of thepasses. are

identical to the location of the passes noted in FIG. 2.

The letters A, B, 'C and D represent successive passes intherefrigeration core.

FIG. 3, shows all the headers mounted externally of the As noted in thedrawing, header 50 is inserted in-" ternally of header 52 and wall 54forms a common wali dividing the two headers. This placing of one headerinside the other with flow in opposite directions is a v unique andnovel wayof accomplishing the desired core temperature distribution.Header 56 is connectedto the. inlet of the evaporator and header 58"isconnected to the V The refrigerant'core element depicted in FIG. 4" is,inmost respects, identical to the core element. shown inFIGSJ 1 and 2,excepttha't internal header 53' connects outlet.

the passages in pass C with 'the passages in pass .D.

What has been shownby this invention is'a novel arrangement of thepasses in therefrigerant' core section of an evaporator which, by virtueofthis arrangement, provides an effective evaporator while permitting'a'reduc-' tion of the overall evaporator size. It will be appreciated thatthis advantage is particularly important in aircraftapplication, sincesize and the attendant reduction in weight increase the overallperformance of-the aircraft. a

It is to be understood that the invention is not limited enema verselyto said channels'formed from first, second, third and fourth finelements and being adapted to place fiuid passing straight: through saidopen-ended channel formed from saidfifth continuous fin element in heatexchange relation to the 'fiuid passing through channels formed fromsaid first, second, thirdand fourth fin elements, so

that the fluid enteringsaid open-ended channel of the fifth A continuousfin element is in immediate heat exchange relation with the fluid insaid first continuous fin element and fluiddischarging frorn saidopen-ended channel of the fifth continuous finelement is in heatexchange relation with the fluid in said thirdcontinuous fin element.

2. A multiplate and fin. core'section of anevaporator i having -a--top"and bottomIclosurc member, a'first' continuous fin element mountedadjacent to said top closure member; a second continuous fin elementmounted adjacent to said first continuous fin element,;a third con- 3:tinuous fin element mounted adjacent, to said second'fin element, and :afourth continuous fin element mounted. ad-

jacent to said third continuous fin element, spaced apart parallelmembers sandwiching the opposite ends of the first, second, third andfourth continuous firr elements and having opposing ends abutting'thetop and bottom closure members defining therewith open channels, meansinter,- connecting said first, second, third. and fou'rth finelementdefining a continuous fiow path for said channels, an inlet header andan outlet header mounted on the evaporator and conducting the flow ofrefrigerant successively through said second, third, fourth and firstcontinuous fin elements, an adjacent passformed from afoontinuous finelement sandwiched between flat plates defininglaterall'y extendingchannels'relative to said first, second, thirdand fourth continuous'finelements for placing fluid in 'heat exchange relationship so thatthe-fluid attheinlet of the adjacent pass is immediatelyinlindirect'heat relation to the fluid in the channels defined by thefirst continuous fin element.--

3. A multichannel, multiplate and fin evaporator comprising at'leastonecontinuous fin element,.spaced apart parallel extending'plate,rnembers. sandwiching the opposite'ends of thefin element for definingtherewith a series.

:" 0f separateparallel openended channels. for receiving a to thespecific embodiment herein illustrated and 'de scribed, but may be' usedin other ways without departing from its spirit as defined by'thefollowing-claims.

I claimf r 1. A multiplate and jfin core section of an evaporator fiuidintended t0 be' cooled, a series of fin elements mounted adjacent one ofsaid parallel, extending plate members, and extending in transverserelationto said one of continuousfin elements for defining four passesfor receiving a refrigerant, other spaced apart parallel extendingplate' members lying transversely to said spaced apart parallelextending plate members, sandwiching the series of fin elements fordefining therewith four. passes, said fourpasses being located one nextto the other such "that the fourth passis'adjacent to the inlet of saidchancomprising a first continuous fin element, a second con-' tinuousfin element located adjacent. to .said first contin-T' uous fin element,a third continuous fin element located adjacent to said secondcontinuous fin element, and a fourth continuous fin element locatedadjacent to said third continuous fin element, spaced plates sandwichingsaid first, second, third and fourthcontinuousfin elements for Idefining parallel channels, closure plate members extending laterallyfrom said .space'd 'plates separating said ffir-st,

second, third and fourth continuous fin elements from each other for,defining'four separate'passes, means for connecting said parallelchannels to each other-to'form a continuous flow path fora refrigerant,an inlet header mounted on the evaporator and havingan opening comnels,the third pass is adjacent the outlet of said channels, the first passis adjacent said fourth pass and said second pass is intermediate-saidfirst pass and said third pass, said passes directing refrigerantsuccessively from the first pass, to the second, pass,.:to thethird passand then the fourth pass. I V 1 a In a 'refrigerant core section of anevaporator having sidewall platesand top and'bottom closure members,

continuous fin. elements extendingbetween said" side wall plates fordefining a series of openended channels, means for separating 'sai'dcontinuous fin elements for defining a pair of'outwardly mounted passesmounted adjacent the bottom and top closure" membersv and inwardlymounted passesmounted between said outwardly mounted passes,

inunicating with one of'said v fin elements, means for connecting saidfirst, second, third andfourth comm nted elements so that saidrefrigerant passes "successively through said, second, third,'fourth.and first continuous 1 fin elements, said evaporator also, having afifth con- V tinuous fin elementdisposed .adjacentfto saidfirst,;second,

third and fourth continuous finelernents, spaced'plates adjacent theedges of saidi-fifth continuous finelement-{j defining therewithopen-ended channels extending; trans ,7 5

an internal headerformed at one endofdthe inwardly mountedl finelements, vand another internal header rnounted on'the oppositeend ofone of said inwardly mounted fin elements and one of said externallymounted .2 fin; elements, an enema header communicating with bothof saidoutwardly mounted fin elements, said internal headers and said externalheaders forminga successive continuous .fiow path throughsaid gchannels,1 an inlet Z; er mounted adjacentto cheer said inwardly m'ounted passesand an outlet header mounted adjacent to the last pass in said flowpath, an adjacent pass formed from a continuous fin element sandwichedbetween spaced parallelly mounted plates defining a plurality ofchannels for passing a fluid in heat exchange relationship with thefiuid in the adjacent series of channels.

5. In a refrigerant core section of an evaporator having side wallplates and top and bottom closure members, continuous fin elementsextending between said side wall plates for defining a series ofopen-ended channels, means separating said continuous fin elements fordefining a pair of outwardly mounted passes mounted adjacent the bottomand top closure members and inwardly mounted passes mounted between saidoutwardly mounted passes, first and second external headers mountedadjacent to one end of said continuous fin elements, a common wallseparating said first external headers, said first external headerconnecting the pair of inwardly mounted passes and the second externalheader connecting the outwardly mounted passes, a third external headermounted adja cent to an inwardly mounted and an outwardly mountedcontinuous fin element and disposed on the opposite end from said firstand second external headers, means for leading fluid through saidchannels and defining a How path through one of said inwardly mountedpasses through one of the external headers through the other inwardlymounted passes, through another externally mounted header, through anoutwardly mounted pass, through another externally mounted header andthrough an outwardly mounted pass, said evaporator having an air coresection comprising of at least one continuous fin element, parallelspaced fiat walls abutting the opposite edges of said fin elementdefining therewith a plurality of openended channels extendingtransverse but adjacent to said open-ended channels in the refrigerantcore section, the inlet end of said open-ended channel in the air coresection disposed adjacent one of said outwardly mounted passes and theoutlet end of said open-ended channel in the air core section disposedadjacent the other of said outwardly mounted passes.

6. In a refrigerant core section of an evaporator having side wallplates and top and bottom closure members, continuous fin elementsextending between said side wall plates for defining open-endedchannels, means separating said continuous fin elements for defining apair of outwardly mounted passes mounted adjacent the bottom and topclosure members and inwardly mounted passes mounted between saidoutwardly mounted passes, first, second and third internal headerslocated in the core section, said first internal header mounted at oneend of the inwardly mounted passes, said second internal header mountedon the opposite end of the inwardly mounted passes and connecting one ofsaid inwardly mounted passes to an outwardly mounted pass, said thirdinternal header mounted adjacent said first internal header andconnecting the outwardly mounted passes with each other, first externalheader leading to an inlet and connected to an inwardly mounted pass forreceiving a refrigerant and a second external header having an outletfor communicating with one of said outwardly mounted passes providing acontinuous refrigerant fiow path from said first external header, to oneof said inwardly mounted passes, to said first internal inlet header, tosaid other inwardly mounted passes, to said third internal header to oneof said outwardly mounted passes, to said second internal header, to theother of said outwardly mounted passes and to said second externalheader, said evaporator having an air core section comprising of atleast one continuous fin element parallel spaced fiat walls abutting theopposite edges of said fin element defining therewith a plurality ofopen-ended channels extending transverse but adjacent to said open-endedchannels in the refrigerant core section, the inlet end of saidopen-ended channel in the air core section disposed adjacent one of saidoutwardly mounted passes and the outlet end of said open-ended channelin the air core section disposed adjacent the other of said outwardlymounted passes.

References Qited by the Examiner UNITED STATES PATENTS 1,139,549 5/15Lovekin 165163 2,875,986 3/59 Holm l65l65 3,043,110 7/62 Ahern 165-145CHARLES SUKALO, Primary Examiner.

FREDERICK L. MATTESON, JR., Examiner.

1. A MULTIPLATE AND FIN CORE SECTION OF AN EVAPORATOR COMPRISING A FIRSTCONTINUOUS FIN ELEMENT, A SECOND CONTINUOUS FIN ELEMENT LOCATED ADJACENTTO SAID FIRST CONTINUOUS FIN ELEMENT, A THIRD CONTINUOUS FIN ELEMENTLOCATED ADJACENT TO SAID SECOND CONTINUOUS FIN ELEMENT, AND A FOURTHCONTINUOUS FIN ELEMENT LOCATED ADJACENT TO SAID THIRD CONTINUOUS FINELEMENT, SPACED PLATES SANDWICHING SAID FIRST, SECOND, THIRD AND FOURTHCONTINUOUS FIN ELEMENTS FOR DEFINING PARALLEL CHANNELS, CLOSURE PLATEMEMBERS EXTENDING LATERALLY FROM SAID SPACED PLATES SEPARATING SAIDFIRST, SECOND, THIRD AND FOURTH CONTINUOUS FIN ELEMENTS FROM EACH OTHERFOR DEFINING FOUR SEPARATE PASSES, MEANS FOR CONNECTING SAID PARALLELCHANNELS TO EACH OTHER TO FORM A CONTINUOUS FLOW PATH FOR A REFRIGERANT,AN INLET HEADER MOUNTED ON THE EVAPORATOR AND HAVING AN OPENINGCOMMUNICATING WITH ONE OF SAID FIN ELEMENTS, MEANS FOR CONNECTING SAIDFIRST, SECOND, THIRD AND FOURTH CONTINUOUS FIN ELEMENTS SO THAT SAIDREFRIGERANT PASSES SUCCESSIVELY THROUGH SAID SECOND, THIRD, FOURTH ANDFIRST CONTINUOUS FIN ELEMENTS, SAID EVAPORATOR ALSO HAVING A FIFTHCONTINUOUS FIN ELEMENT DISPOSED ADJACENT TO SAID FIRST, SECOND, THIRDAND FOURTH CONTINUOUS FIN ELEMENTS, SPACED PLATES ADJACENT THE EDGES OFSAID FIFTH CONTINUOUS FIN ELEMENT DEFINING THEREWITH OPEN-ENDED CHANNELSEXTENDING TRANSVERSELY TO SAID CHANNELS FORMED FORM FIRST, SECOND, THIRDAND FOURTH FIN ELEMENTS AND BEING ADAPTED TO PLACE FLUID PASSINGSTRAIGHT THROUGH SAID OPEN-ENDED CHANNEL FORMED FROM SAID FIFTHCONTINUOUS FIN ELEMENT IN HEAT EXCHANGE RELATION TO THE FLUID PASSINGTHROUGH CHANNELS FORMED FROM SAID FIRST, SECOND, THIRD AND FOURTH FINELEMENTS, SO THAT THE FLUID ENTERING SAID OPEN-ENDED CHANNEL OF THEFIFTH CONTINUOUS FIN ELEMENT IS IN IMMEDIATE HEAT EXCHANGE RELATION WITHTHE FLUID IN SAID FIRST CONTINUOUS FIN ELEMENT AND FLUID DISCHARGINGFROM SAID OPEN-ENDED CHANNEL OF THE FIFTH CONTINUOUS FIN ELEMENT IS INHEAT EXCHANGE RELATION WITH THE FLUID IN SAID THIRD CONTINUOUS FINELEMENT.